The present invention generally relates to electrical discharge detection techniques for structures, and more particularly, to a system, device and method to estimate a condition of a structure due to such electrical discharges.
Various structures, such as, but not limited to, wind turbines, aircrafts, marine structures, communication towers, or other tall structures, may be exposed to electrical discharges due to e.g., lightning strikes. For example, wind turbine blades have become increasingly susceptible to lightning strikes as the dimensions of the wind turbine blades have increased. Moreover, wind turbine blades may be adversely affected when exposed to lightning strikes. Consequently, this can result in reduced productivity since a relatively long period of down-time may be needed to inspect and further repair and/or replace an affected blade or component.
Several lightning detection systems applicable to wind turbines have been proposed in the past. The basic approach in such systems is to provide several magnetic and/or electric field sensors distributed along the length of a rotor blade of the wind turbine and to measure the magnetic and/or electric field concentration along the rotor blade. An evaluation unit connected to the magnetic and/or electric field sensors receives measurement signals thereof, and calculates damage to the wind turbine and, in particular, to the rotor blade caused by a lightning strike. However, an evaluation based on the measured magnetic and/or electric field concentration does not necessarily provide for estimating the condition of individual components or parts of the wind turbine.
In order to address the above need, one common detection system employs magnetic cards positioned on various parts of the wind turbine, wherein a magnetic field generated by a lightning strike marks traces on a magnetic strip of the magnetic card. Such a technique enables reading the maximum lightning current to which the blade was exposed. However, the readings need to be read manually by interrupting the wind turbine operation. Also, the technique does not enable recording of several lightning strikes occurring in a sequence and/or the time of occurrence of the strikes. Furthermore, only the latest of the lightning strikes having the highest magnitude is registered in the magnetic card due to an assumption that a lightning current of high magnitude may lead to a high probability of damage on the structure in comparison to a relatively lower magnitude lightning strike. For example, in the event that a lightning strike having a lightning current of a magnitude lower than a first threshold value, e.g., 30 kA, is discharged, the lightning strike may not be registered on the magnetic card. Conversely, in the event that a lightning strike having a lightning current of a magnitude higher than a second threshold say, about 50 kA, the lightning strike may be registered on the magnetic card. However, a sequence of low magnitude lightning strikes occurring over a period of time may also lead to a potential risk of damage to the structure, but may nonetheless not be recorded.
One attempt to address the drawback associated with the aforementioned magnetic card system may include using electronic storage mediums for registering lightning strikes. However, the need for a constant supply of power to retain stored data renders them incapable of being mounted on rotary components such as the blades of the wind turbine. Although, rechargeable/replaceable batteries may provide the power required by such storage mediums, the need for continuous replacement of the batteries over a period of time makes them unsuitable for remote, off-shore applications where manual intervention is few and far-between.
Therefore, a need exists for an improved lightning detection system that may address one or more of the problems set forth above.